This invention relates generally to a method and apparatus for extinguishing fires and, more particularly, to a method and apparatus for extinguishing fires in storage vessels filled with flammable liquids.
Extinguishing fires in flammable liquid filled vessels is difficult because of the typically very volatile nature of the stored liquids. The techniques generally employed to extinguish such fires, often called tank fires, entail the discharge of an extinguishing agent onto the surface of the burning liquid. Usually, the fire extinguishing agent is released from a portable, manually operated extinguisher. Particularly for fires in large capacity storage tanks, the manual application of a fire extinguishing agent exhibits inconsistent effectiveness and presents the possibility of injury to fire fighting personnel. Those problems are somewhat alleviated with fixed extinguishing systems having electrical controls that are actuated either automatically in response to fire detection or manually by remotely positioned operators. However, fixed systems also exhibit certain disadvantages including the requirement for release of copious quantities of extinguishing agent to insure the presence thereof over the entire exposed surface of the flammable liquid. Even then, the deposition of extinguishing agent over the entire exposed surface of the flammable liquid is rendered difficult by the heavy turbulence inherently associated with fire. This difficulty is accentuated in tank installations having physical obstructions that inhibit the discharge of extinguishing agent onto all surface portions of the flammable liquid. Another problem is that the extinguishing agent, when discharged under pressure, can actually spread a fire by splashing burning fuel out of an open vessel.
Another technique previously suggested for extinguishing tank fires involved the release of CO.sub.2 beneath the surface of the flammable liquid. According to the teachings of that technique, the released CO.sub.2 would rise through the flammable liquid and extinguish a fire burning on its surface. A fire extinguishing method of that type is disclosed, for example, in U.S. Pat. No. 145,134. The subsurface release of CO.sub.2 is impractical for large tank fires, however, because of the inherent condition that a majority of the released agent is absorbed by the flammable liquid. Therefore, most of the released CO.sub.2 fails to reach the surface of the burning liquid and thereby function as an extinguishing agent. For those reasons excessive quantities of CO.sub.2 must be used which is both inefficient and increases the possibility of fire spread due to splashing fuel.
The object of this invention, therefore, is to provide an improved method for extinguishing fires burning above and fueled by a flammable liquid stored in a storage vessel.